The hydrogen-rich gas mixtures recovered from ammonia plant purge, as well as other hydrogen-rich gases obtained as off gas in various industrial processes, typically contain methane accompanied by low-boiling inert gas such as nitrogen and/or argon. Such gas mixtures are generally burned to recover the fuel value of the combustible gases such as hydrogen and methane and that of higher hydrocarbons that may be present. In doing so, however, the higher feed stock value of the hydrogen is sacrificed. A process can be designed to recover a substantial part of the methane and to further upgrade the hydrogen, employing a conventional partial condensation process. A typical example of such proposed partial condensation system is that described in U.S. Pat. No. 3,675,434. In such a partial condensation process, however, only about 20% of the methane is recoverable at a higher heating value (HHV) on the order of 600 Btu/scf (5342 Kcal/m.sup.3). By alternative design modifications using partial condensation techniques, up to about 82% of the methane content of the gas mixture can be recovered but only as a fuel gas product of quite lower heating value, such as that corresponding to the heating value of typical ammonia plant purge gas, which has a higher heating value on the order of about 330 Btu/scf (2938 Kcal/m.sup.3 at 21.degree. C.).
The composition of the ammonia plant purge gas will vary to a certain extent with the process conditions employed and the particular source or sources of the feed gas. In general, however, purge gas will contain, after pre-separation of ammonia therefrom, (in mole percent) about 60-70% hydrogen, about 20 to 30% nitrogen and argon, the remainder being mostly methane. Other hydrogen-rich gas mixtures derived from industrial processes such as in hydrogenation may include, in addition to methane and possibly some higher boiling hydrocarbons, a low boiling elemental gas such as nitrogen and/or argon, and also other gas boiling below methane such as carbon monoxide for example.